The effect of welding residual stresses on brittle fracture in an internal surface cracked pipe

• A Two-pass pipe welding process is simulated and obtained residual stresses (RS) are experimentally verified.
• An internal semi-elliptical circumferential cracked pipe is considered and Modified Beremin model is used.
• Two sets of specimens with high and low crack-tip constraint are used for model calibration.
• Welding RS will cause to change crack-tip stress field and fracture probability, dramatically.
• RS cause 40% increase in maximum opening stress and 38% decrease in fracture toughness, for a fracture probability of 90%.

The change in brittle fracture properties due to the presence of welding residual stresses (RS) is studied in a pipe. Welding RS are simulated by using a 3-D finite element (FE) model and experimentally verified. An internal circumferential thumbnail crack is introduced at the weld line. The modified Beremin model is used as local approach method to predict toughness distributions in the presence of welding RS. The model is calibrated using experimental fracture tests at −150 °C consisting of low and high constraint specimens. The results indicate that, in the welded pipe, the fracture toughness will decrease dramatically in comparison with the as-received pipe. For the same fracture probability of 90%, fracture toughness will decrease from 65 to 40 MPa √m. This is due to the influence of tensile welding RS on the crack tip stress state, which result in a decrease in the opening mode stresses at the near crack tip up to 40%.